An MRI apparatus is an imaging apparatus which magnetically excites nuclear spin of an object placed in a static magnetic field with a radio frequency (RF) pulse having the Larmor frequency and reconstructs an image on the basis of magnetic resonance (MR) signals emitted from the object due to the excitation.
In the field of MRI, there are known imaging methods such as the arterial spin labeling (ASL) method and the phase contrast (PC) method.
The ASL method is an imaging method in which longitudinal magnetization of fluid such as intravascular blood and/or cerebrospinal fluid (CSF) is labeled by a labeling pulse and then MR signals are acquired after a predetermined waiting time by applying an imaging sequence with an excitation pulse. Under the ASL method, it is possible to generate an image in which the position of the labeled fluid after the predetermined waiting time is correctly depicted. Under the ASL method, it is also possible to correctly trace change in the position of the labeled fluid (i.e., movement of the labeled fluid) by performing plural imaging sequences, waiting times of which are different from each other.
However, it is impossible under the ASL method to depict a position and/or movement of unlabeled fluid. Thus, it is difficult to grasp movement of fluid in the entire FOV (Field of View) space from data obtained by the ASL method.
The PC method is an imaging method in which a gradient magnetic field called a velocity encoding pulse is applied posterior to application of each excitation pulse and then each MR signal is acquired by applying a readout gradient pulse. The phase of each MR signal is changed by the velocity encoding pulse depending on velocity of fluid at each position in an FOV (Field of View). As the result, it is possible to obtain velocity information of the fluid for each pixel position in the entire FOV space from phase change of each MR signal acquired by the PC method.
However, information obtained by the PC method is velocity information in an FOV at a certain time. Thus, it is impossible under the PC method to obtain trace information indicative of how specific blood moves in an FOV.
Although the ASL method and the PC method are different in merit and demerit from each other as described above, in conventional technology, each of imaging under the ASL method and imaging under the PC method has been performed by a separate pulse sequence. Thus, in order to obtain respective merits of the ASL method and the PC method, both of imaging under the ASL method and imaging under the PC method are required for generating each image, and thus its total imaging time has become long. Additionally, in the conventional technology, since it has been impossible to perform imaging under the ASL method and imaging under the PC method at the same time, there has been a time gap between execution of the ASL method and execution of the PC method. This time gap causes a risk that behaviors of fluid to be imaged, such as a position and velocity do not coincide between the ASL method and the PC method.